Purification of zinc bearing material solutions containing manganese

ABSTRACT

Disclosed herein is a process for removing at least a portion of a manganese constituent from a zinc-bearng material, comprising the step of subjecting the material to a first oxidation mixture of SO 2  and oxygen, at conditions sufficient to oxidize the manganese constituent

REFERENCE TO CO-PENDING APPLICATIONS

[0001] The subject matter of PCT application serial number PCT/CA00/00352 filed Apr. 5, 2000 entitled PURIFICATION OF ZINC-BEARING MATERIAL SOLUTIONS CONTAINING MANGANESE is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. FIELD OF THE INVENTION

[0003] The present invention relates to the purification of zinc-bearing materials, more particularly but not necessarily exclusively to zinc-bearing aqueous solutions.

[0004] 2. DESCRIPTION OF THE RELATED ART

[0005] Some zinc (Zn) ores, for example sphalerite, contain high levels of manganese (Mn) that cannot be separated using conventional mineral processing techniques, since the Mn is present in the crystal lattice. When Zn sulphides containing Mn impurities are roasted and then leached, they can, in some cases, produce lcach solutions or electrolyte solutions containing unreasonably high levels of Mn.

[0006] Although some relatively small amounts of Mn are generally acceptable in a Zn elecolyte, for example, excessive quantities can create problems, since the Mn is oxidized at the anode in the form of MnO_(2,) some of which falls at the bottom of the cell and must be periodically removed. Greater concentration of MnO₂ can lead to significant reductions in electrolytic efficiency.

[0007] It is generally known in the prior art that precipitating zinc and manganese together, using sodium carbonate or lime as naturalizing agent, can be carried out at 70° C and at pH values between 5 and 7. However, in this case, zinc begins to precipitate before manganese and therefore most of the zinc would be precipitated with manganese which is obviously not acceptable, as shown in FIG. 1.

[0008] Another solution proposed by the prior art is to oxidize Mn²⁺to Mn⁴⁺so that MnO₂ can be removed by precipitation at a pH where Zn²⁺is soluble. Air and oxygen gas are typically used as oxidants in this case but they are generally uneconomically slow. Peroxide or stronger oxidants, such as Caro's acid or ozone, are in many cases too expensive.

[0009] U.S. Pat. 2,816,819 to Wallis et al. discloses a system which uses SO₂ /Air to precipitate iron from a cobalt- or a nickel-bearing solution. Canadian Patent 935,650 discloses a technique by which a mixture of SO₂ /Air is used to precipitate a number of impurities from a cobalt or a nickel solution. However, neither reference is concerned with techniques for reducing impurities from Zn-bearing materials.

[0010] It is an object of the present invention to provide an improved method to remove at least a portion of Mn from Zn-bearing materials.

SUMMARY OF THE INVENTION

[0011] Briefly stated, the invention involves a process for removing at least a portion of a manganese constituent from a zinc-bearing material, comprising the step of Subjecting the material to mixture of SO₂ and oxygen, at conditions sufficient to oxidize the manganese constituent,

[0012] Preferably, the material is maintained at a pH sufficient to precipitate manganese while minimizing precipitation of the zinc constituent.

[0013] In another of its aspects, the present invention provides a process for removing at least a portion of a manganese constituent from a zinc-bearing material, comprising the step of subjecting said material to a first oxidation mixture of SO₂ and oxygen, at conditions sufficient to oxidize said manganese constituent, wherein the material is maintained at a par between 3 and 4 to form a manganese precipitate and no zinc precipitate.

[0014] In still another of its aspects, the preset invention provides a process for removing a manganese impurity from a zinc-bearing solution, comprising the steps of:

[0015] subjecting the solution to a mixture of SO₂ and oxygen, at conditions sufficient to oxidize said manganese constituent as manganese oxide; and

[0016] maintaining the pH of the solution between 3 and 4 to form a manganese with no zinc co-precipitate.

[0017] In still another of its aspects, the preset invention provides an aqueous zinc-bearing solution, comprising the steps of:

[0018] subjecting the solution to a mixture of SO₂and oxygen, at a temperature of between 40° C. and about 80° C. to oxidize said manganese constituent; and

[0019] maintaining the pH of the solution between 3 and 4 to form a manganese with no zinc co-precipitate.

[0020] In still another of its aspects, the preset invention provides a process for removing a manganese impurity from an aqueous zinc-bearing solution, comprising the steps of

[0021] subjecting the solution to a mixture of SO₂and oxygen, at a temperature of between 40° C. and about 80° C. to oxidize said manganese constituent; and

[0022] maintaining the pH of the solution between 3 and 4 to form a manganese with essentially no zinc co-precipitate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Several preferred embodiments of the present invention will now be described, by way of example only, with reference to the appended drawing in which:

[0024]FIG. 1 is a plot of precipitation for Mn and Zn according to pH; and

[0025]FIG. 2 is a plot of precipitation using SO₂/O₂mixture as all oxidant;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Briefly stated, the invention involves a process for removing at least a portion of a manganese constituent from a zinc-bearing material, comprising the step of subjecting the material to mixture of SO₂and oxygen at conditions sufficient to oxidize the manganese constituent.

[0027] Preferably, the material is maintained at a pH sufficient to precipitate manganese while minimizing precipitation of the zinc constituent Preferably, the process is carried out at a pH between about 3 and about 5 more preferably between 3 and 4. Still more preferably, the pH is 3.

[0028] If the pH is higher than 5, for example up to 7, at least some residual Zn may be precipitated with the Mn. The higher the pH in this range, the greater the quantity of Zn being precipitated with Mn. In this case, it may be feasible either to process the Mn subsequently with the residual Zn in place or alternatively to subject the co-precipitate to a mildly acidic solution (such as at a pH of 3 to 4) to re-dissolve the residual zinc.

[0029] The pH limit of 4 is significant because, as the following examples illustrate, residual Zn has been found to appear in the precipitate at a pH value above 4 while there appears to be no Zn co-precipitate at pH values below 4. Therefore, it may be desirable, in some circumstances, to maintain tie reaction at the lower end of the pH rage, that is in the vicinity of pH 3 in order to minimize the likelihood of a Zn co-precipitate. This route may also be enhanced by maintaining a distribution of nucleation sites in the reaction, such as MnO₂crystals.

[0030] The oxygen may be in the form of O₂or air or a mixture of both.

[0031] Preferably, the process occurs at a temperature from about 40 to about 80° C., more preferably at a temperature ranging from 50 to 80° C., still more preferably at a temperature ranging from 58 to 78° C. For example, the process may be carried out al about 70° C. or, alternatively, at about 60° C.

[0032] It may also be desirable, in some cases, to raise the temperature above 80° C., for example to an upper limit of about 130° C. or higher in order to increase the reaction kinetics of the process, though this would need to be done under pressure, depending on the chosen temperature. For example, a temperature of 130° C. would require a pressure of about 50 psi.

[0033] Preferably, in the case where the oxygen is present in the form of O₂gas, the SO₂is at a concentration from about 0.5% to 10%, with the balance O₂gas, more preferably from 1 to 8%, still more preferably at a concentration from 2 to 3%.

[0034] In the case where the oxygen is present in air, the SO₂is preferably at a concentration ranging from about 0.1% to 2%, with the balance being Air, more preferably from about 0.2 to 1.4%, still more preferably from about 0.4 to 0.6%. For example, the concentration may be about 0.5%.

[0035] The zinc material may be in a number of forms including an aqueous solution, such as a leach solution or an electrolyte solution.

[0036] The present process is beneficial in that it makes use of a relatively inexpensive and plentiful oxidant a gas mixture of O₂/SO_(2,) or alternatively Air/ SO_(2,) or still alternatively 100% pure Air can be used together with equivalent amounts of SO_(2,) preferably added as SO₂ in a gaseous or liquid form, or added as a constituent in a solution containing for example, sodium metabisulphite, ammonium metabisulphite, potassium metabisulphite or other suitable forms of metabisulphite.

[0037] Embodiments of the present invention will be described with reference to the following Examples which are presented for illustrative purposes only and are not intended to limit the scope of the invention.

EXAMPLE 1

[0038] A solution containing 5 g/L Mn as MnSO₄ was sparged with a mixture of SO₂, and O₂at different pH levels. The amount of Mn removed at each pH is shown in FIG. 2.

[0039] A comparison can be made between the precipitation of pH's of manganese oxidized with SO₂/O₂as shown in FIG. 2 with the precipitation of zinc as shown in FIG. 1. The Mn is removed from solution at pH levels ranging from about 3 to 5. However, in the region from about 3 to 4, the Mn is removed from solution while the Zn is soluble and therefore remains in solution.

EXAMPLE 2

[0040] A solution containing 18 g/L Mn as MnSO₄was sparged at 60° C. and at a pH of 6.5 with SO₂/O₂mixtures containing 2% (v/v) SO₂. After one hour, 25% of the manganese had precipitated. After 2 hours. 57% of the Mn had precipitated and after 4 hours, 99.5% of the Mn had precipitated. 

1. A process for removing at least a portion of a manganese constituent from a zinc-bearing material, comprising the step of subjecting said material to a first oxidation mixture of SO₂and oxygen, at conditions sufficient to oxidize said manganese constituent.
 2. A process as defined in claim 1 wherein the material is maintained at a pH sufficient to precipitate manganese while minimizing precipitation of said zinc constituent.
 3. A process for removing at least a portion of a manganese constituent from a zinc-bearng material, comprising the step of subjecting said material to a first oxidation mixture of SO₂ and oxygen, at conditions sufficient to oxidize said manganese constituent, wherein the material is maintained at a pH between 3 and 4 to form a manganese precipitate and no zinc precipitate.
 4. A process as defined in claim 3 wherein said pH is
 3. 5. A process as defined in claim 3 wherein said oxygen is in the form of O₂.
 6. A process as defined in claim 3 wherein said oxidation mixture includes Air.
 7. A process as defined in claim 3 wherein the subjecting step occurs at a temperature ranging from about 40 to about 80° C.
 8. A process as defined in claim 7 wherein the subjecting step occurs at a temperature ranging from 50 to 80° C.
 9. A process as defined in claim 8 wherein the subjecting step occurs temperature ranging from 58 to 78° C.
 10. A process as defined in claim 8 wherein the subjecting step occurs at about 70° C.
 11. A process as defined in claim 8 wherein the subjecting step occurs at about 60° C.
 12. A process as defined in claim 5 wherein said SO₂is at a concentration from 0.5% to 10%, with the balance O₂ gas.
 13. A process as defined in claim 12 wherein said SO₂is at a concentration from 1 to 8%.
 14. A process as defined in claim 13 wherein SO₂is at a concentration from 2to 3%.
 15. A process as defined in claim 5 wherein SO₂is at a concentration from 0.1% to 2%, with the balance being Air.
 16. A process as defined in claim 15 wherein said SO₂is at a concentration from 0.2 to 14%.
 17. A process as defined in claim 16 wherein SO₂is at a concentration Drum 0.4 to 0.6%.
 18. A process as defined in claim 5 wherein said zinc bearing material is a leach solution.
 19. A process as defined in claim 5 wherein said zinc material is an electrolyte solution.
 20. A process for removing a manganese impurity from a zinc-bearing solution, comprising the steps of: subjecting the solution to a mixture of SO₂ and oxygen, at conditions sufficient to oxidize said manganese constituent as manganese oxide; and maintaining the pH of the solution between 3 and 4 to form a manganese with essentially no zinc co-precipitate. 